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wlanVHTSIGB

Generate VHT-SIG-B waveform

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Syntax

y= wlanVHTSIGB(cfg)
[y,bits] = wlanVHTSIGB(cfg)
[___ = wlanVHTSIGB(cfg,OversamplingFactor=osf)

Description

y= wlanVHTSIGB(cfg) generates a VHT-SIG-B1 time-domain waveform for the specified transmission parameters. See VHT-SIG-B Processing for waveform generation details.

example

[y,bits] = wlanVHTSIGB(cfg) also outputs VHT-SIG-B information bits.

[___ = wlanVHTSIGB(cfg,OversamplingFactor=osf) generates an oversampled waveform with the specified oversampling factor. For more information about oversampling, see FFT-Based Oversampling.

Examples

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Open Live Script

Generate the VHT-SIG-B waveform for an 80 MHz transmission packet.

Create a VHT configuration object, assign an 80 MHz channel bandwidth, and generate the waveform.

cfgVHT = wlanVHTConfig('ChannelBandwidth','CBW80');
vhtsigb = wlanVHTSIGB(cfgVHT);
size(vhtsigb)
ans = 1×2

   320     1

The 80 MHz waveform has one OFDM symbol and is a total of 320 samples long.

Input Arguments

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Transmission parameters, specified as a wlanVHTConfig object.

Oversampling factor, specified as a scalar greater than or equal to 1. The oversampled cyclic prefix length must be an integer number of samples.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

Output Arguments

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VHT-SIG-B time-domain waveform, returned as an NS-by-NT matrix. NS is the number of time-domain samples and NT is the number of transmit antennas.

NS is proportional to the channel bandwidth.

ChannelBandwidthNS
'CBW20'80
'CBW40'160
'CBW80'320
'CBW160'640

See VHT-SIG-B Processing. for waveform generation details.

Data Types: double
Complex Number Support: Yes

Signaling bits used for VHT-SIG-B field, returned as an Nbits column vector. Nbits is the number of bits.

The number of output bits changes with the channel bandwidth.

ChannelBandwidthNb
'CBW20'26
'CBW40'27
'CBW80'29
'CBW160'29

See VHT-SIG-B Processing. for waveform generation details.

Data Types: int8

More About

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VHT-SIG-B

Receivers use the very high throughput signal B field (VHT-SIG-B) in multi-user scenarios to set up the data rate and to fine-tune MIMO reception. The field uses MCS 0 and consists of a single OFDM symbol.

The VHT-SIG-B field is located between the VHT-LTF and the data portion of the VHT format PPDU.

The VHT-SIG-B field in a VHT packet

The VHT-SIG-B field contains the actual rate and A-MPDU length value per user. For a detailed description of the VHT-SIG-B field, see Section 21.3.8.3.6 of IEEE® Std 802.11™-2016. The number of bits in the VHT-SIG-B field varies with the channel bandwidth. The assignment of the bits depends on whether there is a single user or multiple users. For single user configurations, the same information is available in the L-SIG field, but the VHT-SIG-B field is included for continuity purposes.

Field

VHT MU PPDU Allocation (bits)

VHT SU PPDU Allocation (bits)

Description

 

20 MHz

40 MHz

80 MHz, 160 MHz

20 MHz

40 MHz

80 MHz, 160 MHz

 

VHT-SIG-B

B0-15 (16)

B0-16 (17)

B0-18 (19)

B0-16 (17)

B0-18 (19)

B0-20 (21)

A variable-length field that indicates the size of the data payload in four-byte units. The length of the field depends on the channel bandwidth.

VHT-MCS

B16-19 (4)

B17-20 (4)

B19-22 (4)

N/A

N/A

N/A

A four-bit field that is included for multiuser scenarios only.

Reserved

N/A

N/A

N/A

B17–19 (3)

B19-20 (2)

B21-22 (2)

All ones

Tail

B20-25 (6)

B21-26 (6)

B23-28 (6)

B20-25 (6)

B21-26 (6)

B23-28 (6)

Six zero-bits used to terminate the convolutional code.

Total # bits

26

27

29

26

27

29

 

Bit field repetition

1

2

4

For 160 MHz, the 80 MHz channel is repeated twice.

1

2

4

For 160 MHz, the 80 MHz channel is repeated twice.

 

For a null data packet (NDP), the VHT-SIG-B bits are set according to Table 21-15 of IEEE Std 802.11-2016.

Algorithms

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VHT-SIG-B Processing

The VHT-SIG-B field is used to set up the data rate and to fine-tune MIMO reception. For single user packets, since the length information can be recovered from the L-SIG and VHT-SIG-A field information, it is not strictly required for the receiver to decode the VHT-SIG-B field.

For algorithm details, refer to IEEE Std 802.11ac™-2013 [1], Section 22.3.4.8.

FFT-Based Oversampling

An oversampled signal is a signal sampled at a frequency that is higher than the Nyquist rate. WLAN signals maximize occupied bandwidth by using small guardbands, which can pose problems for anti-imaging and anti-aliasing filters. Oversampling increases the guardband width relative to the total signal bandwidth, which increases the number of samples in the signal.

This function performs oversampling by using a larger IFFT and zero pad when generating an OFDM waveform. This diagram shows the oversampling process for an OFDM waveform with NFFT subcarriers made up of Ng guardband subcarriers on either side of Nst occupied bandwidth subcarriers.

FFT-based oversampling

References

[1] IEEE Std 802.11ac™-2013 IEEE Standard for Information technology — Telecommunications and information exchange between systems — Local and metropolitan area networks — Specific requirements — Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications — Amendment 4: Enhancements for Very High Throughput for Operation in Bands below 6 GHz.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2015b

See Also

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1 IEEE Std 802.11ac-2013 Adapted and reprinted with permission from IEEE. Copyright IEEE 2013. All rights reserved.